This invention relates to a power driven boat or ship capable of decreasing friction with water and more particularly to a boat or ship having a rudder arranged at a particular location and having a novel propeller bearing.
The term "ship" as used herein is intended to designate a boat or ship which comprises a propeller and is driven by power.
FIG. 1 illustrates a conventional ship 1 having a propeller 2 and a rudder 3 behind the propeller. Reference numeral 4 denotes a waterline.
As can be seen from FIG. 1, the rudder 3 is located behind the propeller 2. When the ship is cruising on the water, water flow driven by rotation of the propeller moves faster than other water relative to the ship. The difference in velocity between the water flow driven by the propeller and other water becomes greater as the cruising speed of the ship increases. Under such a condition, it is very disadvantageous to arrange the rudder behind the propeller at a location that the water flows at the maximum speed, as shown in FIG. 1, because the rudder is subjected to the maximum friction of water.
In conventional small ships such as fishing boats, bearings for propeller shafts are generally made of white metal or copper alloys which are lubricated by sea water rather than lubricating oil. Propeller shafts of large ships are fitted thereon with copper alloy sleeves to prevent rust and journaled in bearings made of lignumvitae (hard wood produced in the tropics) with lubrication of sea water. However, the sea water tends to enter the bearings of the propeller shafts. It is important to prevent the entrance of the sea water and to recover the lubricant completely without escaping into the sea.